This 1/2 hertz high selectivity filter was found in the December 1990 issue of Radio Electronics magazine. The source must be symmetrical. The capacitors can be changed for other frequencies.
This circuit is recommended for alarm systems since it has a good output stage. The circuit is...
) Suggested by Philips in a 1968 documentation this circuit has very high 10 ohm on-load voltage...
No information is given about the transformers in this circuit suggested by Motorola in a 1968...